Finished Basement Flooding & Cinder Block Walls - How to Fix

July 7, 2006 3:22 PM

The torrential rains here on the east coast a few weeks ago resulted in some fairly minor flooding in my finished basement - one room floor was completely covered by 1/2" of water (where the leak seems to have originated) , and 2 other rooms were partially covered by the same amount. Have owned the house since 1991 (it was built in the mid-1970's), and we met the original owner a few years ago who said he had done an extremely thorough job water-proofing the lower floor/basement area. Until this incident, we never had a single drop of water come through.

The worst-flooded area has a cinderblock wall. Parts of the cinderblock in one corner, from about 4' up down to the floor, were drenched with water, and you can see streaks of water on some blocks in this area. So I assume water leaked through the cinderblocks from that area, where the blocks were wet.

There were no holes evident anywhere, so I'm amazed so much water could simply - it appears - soak through the blocks in 8-9 hours time, and not reveal any obvious holes for the water to proceed through. (We live on top of a very moderate hill, BTW, so the bottom floor/finished basement area is built into the ground, into where the hill slopes. That is, the basement floor is partly underground and surrounded by land about 2/3's around the front and sides, so the presumeably leaky cinderblock is the barrier between the rooms and the ground here.)

We've had 1-2 heavy rain storms since this incident, but no more leaks have occurred since the prior incident.

So the questions ares:

1) Why did this happen?
2) Do cinder blocks start getting permeable after a number of years?
3) What is the best way to insure this flooding does not happen again if we get days of prolonged and heavy rains another time?
4) Should we get a mason or a waterprooofer or both to patch up the cinderblock?
5) Could we do something to repair it ourselves?
6) Is there a way the walls could be tested for leaks?
7) Is this evidence of more serious problems, such as what?

This was all pretty upsetting, given it was unprecedented in this house and in all of our experience of places with basements.

Thanks for any help on this!

posted by Kellyu to home & garden (11 comments total)

What does your guttering look like? Do the pipes go straight down, or do they curve out at the bottom to send the water away from the house?

We had a near-record 12" of rain in the month of January. I had to go under the house to fire up the heater (ran out of oil) and discovered six inches of water in the crawlspace. I got most of it out with a floodsucker.

We had an inspector in this spring to give us a State Of The House report because we're planning on remodeling. (It's 65 years old.) I asked him about the water and the state of the foundation. He said that the foundation had no cracks, but the gutters were causing the problem -- they were dumping water alongside the foundation, and the water was going under it.
posted by dw at 3:34 PM on July 7, 2006

When you get 24" of rain in two months this will happen. Some easy things to do: the gutter thing as noted above but also check the angle of the ground around your foundation. It should be sloping down and away like this:
\

Not like this:
/

You can simply add dirt and angle it with a shovel.

To seriously waterproof the basement may run as much as 6 or 7 thousand. These folks in Mass have a decent reputation.
posted by jeremias at 4:06 PM on July 7, 2006

There is one absolute answer to your third question: improve the grading around your house. There should be at least a 5-6% slope for at least 8 feet around your entire house. If there isn't, add topsoil against the house to create the slope. Water runs downhill - if you create a downhill slope surrounding your house, you greatly reduce the chance of flooding.

A secondary (and just as important) solution is to ensure that your downspouts divert water from your roof at least a few feet away from your foundation wall, and preferably further. Of course, this only applies if your downspouts drain on to your property, rather than into a municipal sewer system.
posted by gwenzel at 4:50 PM on July 7, 2006

Cinderblock is porous from the day it's manufactured. If water pools up behind it, it will seep through.

So, the thing is to stop water pooling up behind it, by shaping the surfaces around your house so water drains away from your walls instead of sitting next to them and soaking on down.

Now that water *has* pooled up behind your basement walls, you'll be damp and musty for a hell of a long time unless you get somebody in who knows what they're doing and pay them what they're worth.

Sorry - no quick fix.
posted by flabdablet at 6:58 PM on July 7, 2006

You don't say what the floor surface is. If it's carpeted, you'll have to rip it all out, or you'll soon have a serious mold spore farm. If it's concrete, just dry it as quickly as you can, using ventilation.
posted by Kirth Gerson at 7:11 PM on July 7, 2006

Cinderblock is porous, like all other concrete stuff. So it's possible that your foundation is perfectly OK and this was a one time thing due to major amounts of water pressing against it from the outside. But it's worth having an expert check your foundation wall to be sure it's not damaged.

Concerning keeping water out in the future: first check into how your waterproofing is set up right now. For instance, do you have a sump pump, weeping tile or waterproof membrane around the outside of the foundation? Those are the most effective ways to keep your basement dry if water is a chronic problem. Note that applying stuff to the inside of the foundation is not an effective water barrier and is likely a waste of money. Water is controlled by keeping away from the foundation in the first place and moving it away if it does get near (hence the weeping tile, which is a porous tube buried underground that leads either away from the house or to a sump pump that drains it to the sewer).

The major problem here is probably that you still have major dampness down there, which can turn in to mold and wreck your house. This often requires removal of carpet, drywall, and wood studs that would have gotten wet. Seriously, you don't want to live in a house with a mold problem.
posted by drmarcj at 7:38 PM on July 7, 2006

The gutters closest to the area that leaked had a plastic pipe attached to it (loosely) that seemed to have leaked, so more watre got in around the edges than would have if it di not leak. The floor where it all poured into is, fortunately, concrete. We got everything very dry, running fans and dehumidifiers for days 24 hrs.
posted by Kellyu at 10:31 PM on July 7, 2006

Occasionally leaky and overflowing gutters are just a fact of life, especially when you get unexpected huge downpours. That's why it's worth paying attention to surface drainage near walls as well.

If you dig a wide, shallow, free-draining trench on the uphill side of your house and around the sides, positioned to catch any water that overflows from your guttering or comes out of leaky downpipes and direct it away from your walls, things will improve quite a bit. You can also try planting a stand of something deep-rooted near the wall that got soaked, to discourage a buildup of water there over time.

Waterproofing below-grade masonry walls is done during construction, before the soil is backfilled against the wall. Proper waterproofing has two components: (1) some kind of impermeable membrane applied to the outside of the wall - this can be plastic film (preferably multiple layers) or a sealant coating or bentonite panels or a combination, and has to make a continuous seal with the waterproofing membrane underneath the floor slab; (2) sand, gravel and drainage to prevent water from pooling outside the wall. If both these things have not been done, nothing you apply to the inside of a below-grade wall is going to help in the long term.

Did your original owner say how his thorough waterproofing was done? Because if it was done as an add-on after the house was built, and it didn't involve excavating outside the walls, it's likely to be useless regardless of how thorough it was.

And I suspect you're going to need that dehumidifier running for a good while yet. It takes a long time to air-dry a damp concrete wall and floor with who knows how much wet soil behind and underneath them.
posted by flabdablet at 12:40 AM on July 8, 2006

The original owner didn't say how he did waterproofed it, but he spoke about it in a way that sounded extremely confident, and I think he said something about it being the only house on the block that (at the time) did not have problem as a result.

You're right about running that dehumidifies - it's taking quite a doggone while to dry it out.
posted by Kellyu at 7:31 PM on July 9, 2006

I'm thinking that what you may, in effect, be trying to do is drain a swimming pool with a drinking straw.

How far below ground level is the floor of your basement? It might be worth your while digging a hole in the ground just outside your wet wall, and seeing if it turns into a well. If it does, you could drop a bilge pump down it for a few weeks, which would give your porous wall and dehumidifier much less work to do.
posted by flabdablet at 7:55 PM on July 9, 2006

Front of the house is 6-8 feet down, in a slope. The back of the house is not underground, as the slope opens up there.

Your idea sounds good, though a bit of work. But I like digging holes for some strange reason.
posted by Kellyu at 10:47 AM on July 11, 2006